The influence of beneficiation on the petrographic, geochemical & physical properties of metallurgical coal from the Soutpansberg Coalfield, South Africa

Abstract

The Soutpansberg Coalfield hosts South Africa's Hard Coking Coal (HCC) reserves, however it is relatively understudied and underdeveloped compared to other coalfields in the country. The Makhado Project, located within the central Tshipise sub-basin of the Soutpansberg Coalfield, is the current focus for the re-establishment of Hard Coking Coal production in South Africa by MC Mining Limited.

This study investigated the properties of a 10% ash metallurgical coal product derived from the beneficiation of a wide diameter drill core (LD57) from the Soutpansberg Coalfield, South Africa. The research was conducted in two parts. Part one of the research entailed testing of LD57 by means of drop shatter, dry tumble and wet tumble tests to estimate the breakage expected during the transportation, handling and processing of the coals. Float-sink testing was conducted to determine suitable washability conditions for the production of a primary metallurgical product of 10% ash content. The fine size fraction (1+0.25 mm) floats yielded the desired 10% ash metallurgical product hence, the fine size fraction floats were selected for further characterisation in terms of their petrographic and geochemical properties in Part two of the research. These fine-sized float samples were analysed for their petrographic composition, coal quality (proximate analyses and total sulphur), mineralogy (X-Ray Diffraction), trace element and rare earth element (REE) composition (X-Ray Fluorescence and Inductively Coupled Plasma Mass Spectrometry), and carbonization (Free Swelling Index) properties.

The breakage tests indicate partitioning of daughter particles will be predominantly into coarse particles, 60% on average. The washability analysis shows clean coal for the desired 10% ash metallurgical product could theoretically be obtained in the 1+0.25 mm size fraction of the Makhado seams, with yields up to 78% at 1.55-1.70 g/cm3 . Simple to moderate separation conditions at ± 0.10 NGM are predicted under these separation parameters.

The fine float samples (metallurgical product) are classified as Medium Rank Bituminous C coals (0.88 %RoV) and are highly vitrinitic in composition (97 vol% mmf). All 1+0.25 mm samples reported FSI values of 9. However, further beneficiation of these samples is necessary for minor reduction of the sulphur content, alkali content and phosphorus content to acceptable industry standards for metallurgical coal. Trace element and REE concentrations in the ashed fine float samples are highly enriched relative to the crustal abundance values. Furthermore, all but samples SU and SMU were found to be a promising source of REE as the total REE concentrations exceeded the 1000 ppm cut-off grade